1. Field of the Invention
The present invention relates to a terminal to be connected for current conduction with an insulated electric wire by way of an ultrasonic connection using ultrasonic energy, and to an ultrasonic connection structure in which such a terminal is connected to an insulated electric wire by means of ultrasonic energy.
2. Description of Relevant Art
Techniques for ultrasonic connection have been disclosed in Japanese Patent Publication No. 7-70345. FIGS. 1A to 1D illustrate the techniques, which employ a pair of opposing plate members that FIG. 1A shows as a first member 1 and a second member 2. The first and second members 1, 2 are made of an ultrasonically weldable plastic material. The first member 1 is formed with grooves 3, and the second member 2, with protrusions 4 to be fitted in the grooves 3.
FIGS. 1B and 1C illustrate an intermediate step of the ultrasonic connection, where a respective groove 3 of the first member 1 receives a terminal 7 and an insulated electric wire 8 to be put thereon. The groove 3 has small concave parts 3a at its bottom. An opposing protrusion 4 has on its vertex face corresponding small convex parts 4a engageable with the concave parts 3a.
As in FIGS. 1B and 1C, the terminal 7 is laid along the bottom of groove 3, and the insulated electric wire 8 is put thereon. Then, the second member 2 is mated to the first member 1 so that the protrusions 4 fit in the grooves 3. Then, with pressures acting between the first and second members 1, 2, ultrasonic vibrations are applied therebetween, causing an insulating cover of the electric wire 8 to be melted between protrusion 4 and groove 3, having its core wire current-conductively contacted to the terminal 7. Concurrently, the first and second members 1, 2 are welded together into an integral connection structure, like FIG. 1D.
In the conventional ultrasonic connection, the terminal 7 and the core wire have a conductive contact secured therebetween, as they are pressed together by a pair of upper and lower welded members 1, 2, which however are made of a resin that shrinks when the temperature is low. FIG. 2 illustrates such a situation, where the pressing tendency is reduced with counteracting forces P1, P2 due to a shrunk protrusion 4 in a groove 3, causing an increased contact resistance between a terminal 7 and a core wire 8a.